Coating compositions containing fluorocarbon polymer monobasic phosphates and phosphoric acid

ABSTRACT

A COMPOSITION FOR PRIMING A SURFACE TO IMPROVE THE ADHESION OF A FLUOROCARBON POLYMER TOPCOAT. THE COMPOSITION CONTAINS ABOUT 50-90% FLUOROCARBON POLYMER BY WEIGHT AND 10-50% MONOBASIC CALCIUM PHOSPHATE AND PHOSPHORIC ACID BY WEIGHT AND A LIQUID CARRIER.

United States Patent O 3,634,353 COATING COMPOSITIONS CONTAINING FLUORO-CARBON POLYMER, MON OBASIC PHOSPHATES AND PHOSPHORIC ACID Clifford HughStrolle, Springfield, Pa., assignor to E. I. du Pont de'iNemours andCompany, Wilmington, Del. No Drawing. Filed Nov. 3, 1969, Ser. No.873,622 Int. Cl. C08f 45/24 U.S. Cl. 260-29.6 F 8 Claims ABSTRACT OF THEDISCLOSURE A composition for priming a surface to improve the adhesibnof a fluorocarbon polymer topcoat. The composition contains about 50-90%fluorocarbon polymer by weight and-50% monobasic calcium phosphate andphosphoric acid by weight and a liquid carrier.

BACKGROUND OF THE INVENTION This invention relates to coatingcompositions. It is specifically concerned with primer compositions forimproving the adhesion of fluorocarbon polymer coatings to theirsubstrates.

The fluorocarbon polymer coatings when applied to metal, glass orsimilar type substrates have somewhat less than desirable adhesivetraits between the fluorocarbon polymer coatings and the substrate.Therefore, a need developed for a primer composition which would improveadhesion.

SUMMARY OF THE INVENTION This invention comprises a primer compositionconsisting of (1) particulate fluorocarbon polymer, (2) monobasiccalcium phosphate and phosphoric acid and (3) liquid carrier. Thisprimer composition is used to prime the substrate before thefluorocarbon polymer topcoat is applied.

The fluorocarbon polymers are known polymers. They include hydrocarbonmonomers completely or partially substituted with fluorine atoms or acombination of fluorine atoms and chlorine atoms. Included in this groupare polytetrafluoroethylene, copolymers of tetrafluoroethylene andhex'afluoropropylene in all monomer unit ratios, and fluorochlorocarbonpolymers such as polymonochlorotrifluoroethylene.Polytetrafluoroethylene is preferred.

The monobasic calcium phosphate is dispersed in an aqueous solution with50% solids by weight. The calcium ion may be replaced by manganese,strontium or any other similar divalent metal ions. However, thedivalent metal ion preferred is calcium.

The phosphoric acid is dispersed in an aqueous solution whichis 85%phosphoric acid by weight. Metaphosphoric or orthophosphoric acid may beused. However, the preferred phosphoric acid is Orthophosphoric acid.

The liquid carrier may be water" or an organic liquid miscible withwater, such as, ethanol, isopropanol, acetone or a Cellosolve. Water ispreferred.

The fluorocarbon polymer ordinarily present in the compositionconstitutes about 50% through 90% by weight of the monobasic calciumphosphate, phosphoric acid and fluorocarbon polymer solids, preferablyfrom about 65% through 75%.

The monobasic calcium phosphate ordinarily present in the compositionconstitutes about 10% through 50% by weight of the monobasic calciumphosphate, phosphoric acid and fluorocarbon polymer solids, preferablyfrom about through 25%.

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The phosphoric acid ordinarily present in the composition constitutesabout 5% through 40% by weight of the monobasic calcium phosphate,phosphoric acid and fluorocarbon polymer solids, preferably from about5% through 15%.

The liquid carrier is ordinarily present in the composition at a ratioof about 5% through 50% by weight of the total composition andpreferably from 15% through 35%.

The composition is made by mixing in an aqueous solution proper amountsof a fluorocarbon polymer, monobasic calcium phosphate and phosphoricacid.

The resulting primer composition can be applied by spraying, brushing,clipping or roller-coating. If the surface to be coated is metal, it ispreferably pretreated by grit-blasting, by the flame spraying of metalsor metal oxides, or by frit-coating the substrate after application, theprimer coat is air-dried and then baked at 450 for 20 minutes.

This primer coat is then topcoated with a conventional clear orpigmented fluorocarbon polymer enamel, and baked in the usual way, togive an adherent fluoropolymer coating.

The composition is most useful for priming metal or glass cookware forcoating with polytetrafluoroethylene. This primer can also be used toprime many similar type articles for coating withpolytetrafluoroethylene. Polytetrafluoroethylene sheeting that has beenprimed with this material can be bonded to other materials such asmetals, plastics or glass.

As a specific example of the composition of this invention the followingillustrative examples are given. In these examples all parts are byweight.

EXAMPLE 1 A primer composition may be prepared by thoroughly mixingMonobasic calcium phosphate dispersion (50% solids) in water 21.5Orthophosphoric acid 4.2 Pigment dispersion (30% solids) in water 13.1Surfactant (available as Du Pouts Duponol) (30% solids)Polytetrafluoroethylene aqueous dispersion (60% solids) 59.2

An aluminum sheet is cleaned. The sheet is then sprayed with the primercomposition to a thickness 0.2 to 0.3 mil (dry). The sheet is then bakedfor 20 minutes at 450 F. after which it is topcoated with a dispersionof polytetrafluoroethylene having the following composition:

Polytetrafluoroethylene non-ionic aqueous disper- The topcoat is sprayedover the primer to a total thickness of 1.2 to 1.4 mils (dry) and thenbaked at 750 F. for 20 minutes.

The resulting coating of olytetrafluoroethylene adheres well to thealuminum substrate.

3 4 The invention claimed is: 4. The composition of claim 2 wherein thefluorocar- 1. A composition consisting essentially of bon polymer ispolytetrafluoroethylene. (a) from 50% through 90% by weight ofparticulate S. The composition of claim 1 wherein the phosphoricfluorocarbon polymer; acid is orthophosphoric acid. (b) from 10% through50% by weight of monobasic 6. The composition of claim 2 wherein thephosphoric calcium phosphate, the percentages by weight being acid isorthophosphoric acid. based on the combined weight of the solids of 7.The composition of claim 1 wherein the liquid carsaid fluorocarbonpolymer, monobasic calcium phosrier is water. phoric acid; 8. Thecomposition of claim 2 wherein the liquid car- (c) from 5% through 40%by weight of phosphoric rier is water.

acid, the percentages by weight being based on the References Citedcombined weight of the solids of said fluorocarbon UNITED STATES PATENTSpolymer, monobasic calcium phosphate and phosn 2 562 118 7/1951 Osdal26029.6 PhOI'lC ac1d, and

. 2,917,476 12/1959 Peterson et al. 260-29.6

(d) a liquid carrier selected from the group consisting 15 3,213,05010/1965 Rice 260 29 6 of water and water miscible liquids. 2. Thecomposition of claim 1 containing from 65% through 75% fluorocarbon, 15%through of mono- HAROLD ANDERSON Primary Examiner basic calciumphosphate, 5% through 15% phosphoric US Cl XR acid, and from 5% throughliquid carier. 20

3. The composition of claim 1 wherein the fluorocarbon 117-46 124 132OF, 138-8 UP; MP, polymer is polytetrafluoroethylene.

. 3 UNITED STATES PATENT OFFICE CE TRIIFICATE 0F CORRECTION Patent No. 5Dated January 11, 1972 ln ventofls) Clifford Hugh Strolle It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 3, line 8, after "calcium" insert phosphate and Signed and sealedthis 18th day of July 1 972.

SEAL) Attest:

EDWARD M .FLETCHER JR ROBERT GQTTSCHALK hAttesting Officer Commissionerof Patents

